MI6 obtained vital secrets from a spy operating at the very heart of Hitler’s high command during the most crucial years of the war, newly discovered intelligence documents have revealed.

The secret agent, code-named “Knopf”, furnished the intelligence service with information on Hitler’s plans in the Mediterranean and on the Eastern Front, the health of Field Marshal Erwin Rommel and even the location of the “Wolf’s Lair” — the Führer’s headquarters in Eastern Prussia.

Historians have tended to play down the wartime role of MI6 — in comparison with the crucial importance of the messages decoded at Bletchley Park — but the discovery of Agent Knopf by the Cambridge historian Paul Winter shows that Britain obtained accurate and highly valuable intelligence from a network of agents in the upper ranks of the Third Reich.

The documents, uncovered in the Churchill Archives in Cambridge and the National Archives, show that Knopf and his sub-agents alerted British Intelligence to German plans for an invasion of Malta in 1942, relayed Rommel’s intentions in North Africa and revealed Hitler’s fatal obsession with capturing Stalingrad on the Eastern Front.